Class GammaDistr

java.lang.Object

random.AbstractDistribution

random.GammaDistr

All Implemented Interfaces:

Distribution, StorableDistribution

public class GammaDistr
extends AbstractDistribution
implements Distribution

This is the Gamma distribution (see the constructor description for its pdf definition).

Copyright (c) 2003
Politecnico di Milano - dipartimento di Elettronica e Informazione

Author:

Fabrizio Frontera - ffrontera@yahoo.it, Modified by Stefano Omini, 7/5/2004

Field Summary

Fields inherited from class AbstractDistribution

engine

Constructor Summary

Constructors

Constructor	Description
GammaDistr()	This is the constructor.

Method Summary

Modifier and Type	Method	Description
double	cdf(double x, Parameter p)	This method is used to obtain from the distribution its cumulative distribution function evaluated where required by the user.
double	nextRand(Parameter p)	This method is used to obtain from the distribution the next number distributed according to the distribution parameter.
double	pdf(double x, Parameter p)	This method is used to obtain from the distribution its probability distribution function evaluated where required by the user.
double	theorMean(Parameter p)	This method is used to obtain from the distribution the value of its own theoretic mean.
double	theorVariance(Parameter p)	This method is used to obtain from the distribution the value of its own theoretic variance.

Methods inherited from class AbstractDistribution

setRandomEngine

Methods inherited from class Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Methods inherited from interface Distribution

setRandomEngine

Constructor Details

GammaDistr

public GammaDistr()

This is the constructor. It creates a new gamma distribution which is defined from pdf:

              (alpha-1)    (-x/beta)
pdf(x) = k * x          * e

with k = 1/(g(alpha) * b^a where g() is the "Eulero" function.

Method Details

pdf

public double pdf(double x,
 Parameter p)
           throws IncorrectDistributionParameterException

This method is used to obtain from the distribution its probability distribution function evaluated where required by the user.

Specified by:

pdf in interface Distribution

Parameters:

x - double indicating where to evaluate the pdf.

p - parameter of the gamma distribution.

Returns:

double with the probability distribution function evaluated in x.

Throws:

IncorrectDistributionParameterException

cdf

public double cdf(double x,
 Parameter p)
           throws IncorrectDistributionParameterException

This method is used to obtain from the distribution its cumulative distribution function evaluated where required by the user.

Specified by:

cdf in interface Distribution

Parameters:

x - double indicating where to evaluate the cdf.

p - parameter of the gamma distribution.

Returns:

double with the cumulative distribution function evaluated in x.

Throws:

IncorrectDistributionParameterException

theorMean

public double theorMean(Parameter p)
                 throws IncorrectDistributionParameterException

This method is used to obtain from the distribution the value of its own theoretic mean.

Specified by:

theorMean in interface Distribution

Parameters:

p - parameter of the gamma distribution.

Returns:

double with the theoretic mean of the distribution. the theoretic mean of the gamma distribution is calculated as alpha/lambda.

Throws:

IncorrectDistributionParameterException

theorVariance

public double theorVariance(Parameter p)
                     throws IncorrectDistributionParameterException

This method is used to obtain from the distribution the value of its own theoretic variance.

Specified by:

theorVariance in interface Distribution

Parameters:

p - parameter of the gamma distribution.

Returns:

double with the theoretic variance of the distribution. the variance of the gamma distribution is calculated as alpha/(lambda^2).

Throws:

IncorrectDistributionParameterException

nextRand

public double nextRand(Parameter p)
                throws IncorrectDistributionParameterException

This method is used to obtain from the distribution the next number distributed according to the distribution parameter.

Specified by:

nextRand in interface Distribution

Parameters:

p - parameter of the gamma distribution.

Returns:

double with the next random number of this distribution.

Throws:

IncorrectDistributionParameterException